In recent years, the development of power storage devices such as a lithium-ion secondary battery and a lithium-ion capacitor has been conducted.
With the development of power storage devices, as a positive electrode active material of lithium-ion secondary batteries, a material which can supply lithium stably has been developed.
For example, as a lithium supply source, a compound containing lithium (Li) and cobalt (Co), such as lithium cobalt oxide (LiCoO2), is known (see Patent Document 1).